This invention relates to a process and apparatus for reducing and smelting iron ore and generating syngas of a controlled high quality composition.
Petroleum has been regarded as the center of any future energy crisis. To assure the future supply of energy, technologies for converting carbon containing materials such as biomass and coal to liquid fuels have long been investigated due to their vast abundance. Gasification of biomass and coal to a gas product rich in carbon monoxide and hydrogen is typically the first step of the conversion. The conventional gasification process involves the partial oxidation of the carbon containing materials with oxygen separated from the air. The reactor is commonly an autoclave that can facilitate the high pressure and high temperature reactions.
Both the air separator for oxygen production and the high pressure-high temperature reactor involve high capital and operation costs, and thus make such gasification a very expensive process.
The gasification product usually contains 10%-30% carbon dioxide in addition to the carbon monoxide and hydrogen. Carbon dioxide needs to be removed to yield a syngas product that is almost entirely made up of carbon monoxide and hydrogen. Syngas is the starting material for many chemical reactions that lead to the production of many useful chemical compounds such as gasoline, diesel, plastics, fertilizers, and other substances.
The current syngas generation technologies typically rely on combustion of a fuel to heat materials.
U.S. Pat. No. 7,381,230 discloses a process for the production of syngas from a feed stream comprising a hydrocarbon containing gas and an oxygen containing gas.
U.S. Pat. No. 7,452,392 discloses a process for the conversion of organic waste material such as municipal trash, sewage, post-consumer refuse, and biomass into syngas.
U.S. Pat. No. 7,717,971 discloses a process for the production of syngas from a hydrocarbon feed stock using a steam reforming system.
U.S. Pat. No. 7,736,400 discloses a method for producing a gas comprising substantial amounts of methane, hydrogen and/or carbon monoxide from a solid carbonaceous material and an oxygen carrier using a non-thermal plasma reactor at a temperature in a range of about 300° C. to 700° C.
U.S. Pat. No. 7,658,155 discloses a process for treatment of waste by gasification in the presence of oxygen end steam or pyrolysis to produce an offgas and treating the offgas in a separated plasma unit in the presence of oxygen and steam.
U.S. patent application Ser. No. 20080277265 discloses a process for reformulating an initial gas into a reformulated gas having designed for characteristics by applying a gas energizing field sufficient to reformulate the majority of the gaseous molecules into their constituents and promoting efficient process acceleration for the reformulation of the constituents into a reformulated gas of designed for characteristics.
Published U.S. patent application Ser. No. 20080069765 discloses a method for catalytic partial oxidation of hydrocarbons with an oxygen containing gas to produce syngas.
Published U.S. patent application Ser. No. 20060228294 discloses a method for producing syngas using a molten metal bath by injecting feed materials directly into the molten metal bath, injecting oxygen and steam into the vessel enclosing the molten metal bath, removing produced syngas continuously, and removing molten metal and vitreous material periodically.
Published U.S. patent application Ser. No. 20070102279 discloses a method tor reducing organic compounds into carbon and gases by microwave energy.
Published U.S. patent application Ser. No. 20060124445 discloses an electrical heating reactor for hydrocarbon gas reforming by passing the hydrocarbon gas and an oxidant gas through a porous but electrically conductive lining material connected between two electrodes. An electrical source is used to power the electrodes and resulting in generation of an electronic flux in the conductive lining and heating the lining.
Published U.S. patent application Ser. No. 20050191233 discloses a process for catalytic partial oxidation of hydrocarbons to produce a syngas.
The above patents or published patent applications teach only syngas productions from carbonaceous or organic materials, and do not describe co-production of syngas and metal.
U.S. Pat. No. 7,674,443 discloses an integrated process for gasifying a carbonaceous source using steam and oxygen gas and producing nanoscale metallurgical powder through carbochlorination using chlorine gas as a reacting and carbon monoxide as an oxygen sink.
U.S. published patent application Ser. No. 2002177745 discloses a method for processing waste materials into more desirable products by the expedient of breaking down these materials into their stable molecular constituents and reforming them into more desirable substances in two chambers with microwave radiation, lasers, masers, and/or ultrasonic energy.
Currently, steels are produced by two types of operations: integrated mills and minimills. In the integrated mill, sintered iron ore pellets, coke and lime are charged into a blast furnace (BF). Air is blown at high speed to combust the coke to generate carbon monoxide and heat. Sintered iron ore pellets are reduced to hot metal by carbon monoxide and melted to form liquid pig iron. The liquid iron is then sent to a basic oxygen furnace (BOF) where pure oxygen is blown into the liquid iron to remove excessive carbon and convert the iron into steel. The fundamental problems associated with this production route are the needs for coke and intensified combustions. Coke making is one of the most polluting of industrial processes and intensified combustion generates a great amount dust and waste lot of energy in the exhaust gases.
Minimills employ electric arc furnaces (EAF) to melt steel scrap and/or DRI (direct reduced iron) and produce generally lower quality steel. Minimills traditionally enjoyed an abundant supply of steel scrap. However, recent rapid economic growth of major developing countries has caused shortage of steel scrap supply.
Currently, DRI is produced by three types of processes: gas/shaft, gas/fluid bed, and Coal/RHF (rotary hearth furnace) or RKF (rotary kiln furnace). In a gas/shaft process such as Midrex or HYL, iron ore powder is heated and reduced into iron powder in a shaft with a hot reducing gas which is derived from reforming natural gas. In a gas/fluid bed process such as Fior or FINMET, iron ore powder is heated and reduced into iron powder in a series of fluidized-bed reactors with a hot reducing gas which is also derived from reforming natural gas, In a coal/RHF or RKF process such as FASTMET or INMETCO, pellets of iron ore and carbonaceous powders are heated by combustion of a fuel in a rotary hearth furnace or a rotary kiln. The carbonaceous material functions as the reducing agent to reduce the iron ore pellets into iron sponges. The gas/shaft process dominates the DRI production at present. The price and uncertain supply of natural gas have caused operational difficulties in many DRI plants.
In addition to producing DRI by solid reaction, there are several iron smelting processes such as COREX, Hismelt and Mesabi Nugget which produce molten iron or involve iron smelting using coal, natural gas or oil as the combustion fuel or heating source.
All of the above technologies rely on external heating of the materials through conduction, convection and radiation from a heating source.
U.S. Pat. No. 4,906,290 discloses a method of drying and heating a mixture of particulate ores with an oxygen-containing carbonaceous material using microwave energy to initiate reduction reaction of the ores. In this method, solid oxide wastes can be treated in the same manner as the particulate ores to recover selected elements.
U.S. Pat. No. 6,277,168 discloses a new steelmaking technology based on the use of microwave energy. This technology can produce DRI, iron or steel from a mixture, consisting of iron oxide fines, powdered carbon and fluxing agents. This technology is projected to eliminate many current intermediate steelmaking steps, such as coking, sintering, BF ironmaking, and BOF steelmaking. In this technology, Zn, Pb, Sn, Cd and Fe bearing by-products such as BOF sludge and EAF dust can be treated in a similar manner as iron ore concentrates to extract valuable metals.
Published U.S. patent application Ser. No. 2004/70060387 discloses a process for the reduction of a metalliferous ore or concentrate using a microwave induced plasma.
PCT/AU88/00437 discloses a method for microwave irradiation of mineral ores and concentrates to produce metallic droplets.
All of the above patents and patent applications have no concurrent steel and gaseous fuel production.
Steelmaking by-products such as EAF dust and BOF sludge cannot be disposed directly because both by-products contain high level of zinc and the highly toxic lead and cadmium. Several THMR (high temperature metal recovery) technologies have been disclosed to teach the methods of treating the by-products by heating them with a combustion source in a reducing condition in a furnace. The zinc and cadmium exist in the form of oxides which are be reduced, volatized, re-oxidized and captured b a gag house connected to the furnace exhaust. The most successful of the HTMR technologies is the Waelz kiln process.
U.S. patent application Ser. No. 10/950,260 filed on Sep. 24, 2004, now U.S. Pat. No. 7,227,882 teaches a method of preheating a mixture of EAF dust and a quantity of carbon to between 100° C. and 200° C. with a conventional heating method. The preheated dust is then heated by microwave in a microwave compatible kiln until zinc in the preheated dust vaporized to form a metal vapor and a residue. The zinc vapor is then condensed or oxidized and captured by a bag house. The residue is removed from the microwave kiln and further heated to form a molten material. The quantity of carbon is determined by the percentage of zinc.
There is no syngas produced in the process described in that application.
In published international application Ser. No. WO 2008/051356 by the present inventors, there is a suggestion of producing syngas after an initial reduction of iron oxide using microwave energy and carbon preferably coal as a reducing agent. The syngas is comprised of CO produced by a reaction of excess carbon and oxygen released from the iron oxide in being reduced in a first microwave heating zone and H2 produced from hydrocarbons and moisture in the coal in a second zone of heating, both reactions enhanced by the presence of metallic iron produced by the reduction of iron oxide.
However, it would be desirable to control the composition of the syngas to insure a major H2 component as well as CO to which is easily convertible to liquid fuels such as gasoline.
It is an object of the present invention to improve the methods and apparatus described in PCT WO 2008/051356 by increasing their efficiency and output and to produce a high quality syngas able to be easily converted to liquid fuels, and also to include an ability to control the composition of such high quality syngas.